1. Field of the Invention
The present invention relates to a scanning micro-lithographic apparatus and method for projecting a large field-of-view image on a substrate and, more particularly, to such apparatus that preferably employs a wide-field catadioptric projection system (e.g., a projection system incorporating a Wynne Dyson optical relay).
2. Description of the Prior Art
Some micro-lithographic applications, like flat display panel manufacturing, require a fast, seamless, high-resolution (e.g., 2-3 micrometers), large area exposure. This kind of exposure can be achieved effectively by scanning the substrate under a large exposure projection system with a field-of-view for exposure.
It is well known that micro-lithography can be done over a large area by combining two xe2x88x921X projection systems having parallel object and image planes with a raster scanning system that moves the mask and substrate together so as to produce one strip of imagery at a time. The precision requirements on the scanning system are relaxed if adjacent strips of imagery are not butted together, but overlapped in a small area containing a linear variation in exposure intensity, such as can be obtained using a tapered illumination slit. A micro-lithography approach employing this principle is described in U.S. Pat. No. 5,298,939 and its division U.S. Pat. No. 5,835,195, both of which are entitled xe2x80x9cMethod and Apparatus for Transfer of a Reticle Pattern onto a Substrate by Scanningxe2x80x9d. The drawback with this approach is that to obtain a +1X relay system it is either necessary to employ two xe2x88x921X relays in series or to add an odd number of folds to the optical system which is often inconvenient or impossible. Also the requirements on the raster scanning system lead to substantial expense and complexity in the stage components.
An alternate approach, described in U.S. Pat. No. 5,585,972, entitled xe2x80x9cArbitrarily Wide Lens Array with an Image Field to Span the Width of a Substrate,xe2x80x9d employs an array of +1X projection systems, which span the width of the substrate, to reduce the scanning requirement to a single linear scan. The drawback with this approach is that it requires a great many projection optical systems all of which have to be aligned very accurately and the illumination apertures are a staggered array of rectangles which is difficult to illuminate uniformly.
Therefore, there is a need for a scanning micro-lithographic apparatus and method that derives a high-resolution, large area exposure over a large area with a greatly simplified projection and illumination optical system, while not introducing too much complexity in the scanning system. In this regard, the teachings of U.S. Pat. No. 5,852,693, entitled xe2x80x9cLow-loss Light Redirection Apparatusxe2x80x9d which discloses a uniform illumination system employing light guiding technology using multiple light-pipes, is incorporated herein by reference.
The present invention is directed to a scanning micro-lithographic apparatus that employs a fixed xe2x88x921X projection system (preferably, a wide-field catadioptric projection system) having a limited field of view in which image patterns located in its object plane can be imaged onto a substrate located in its image plane. These patterns, which are contained on a reticle or mask, are wider than the limited field size of the projection system. The mask is illuminated over the area corresponding to the field of the projection system and is moved in the object plane reticle in a direction parallel to that in which a vector in the object plane would be imaged parallel to its image in the object plane. Synchronous motion of the substrate in the same direction, scanning, copies the pattern from the reticle onto the substrate. In this fashion, a strip of imagery spanning the length of the pattern on the reticle may be copied onto the substrate. Other strips of imagery may be added in subsequent scans but, because the magnification is xe2x88x921X, it is necessary to re-register the reticle and substrate by stepping them equally in opposite directions normal to the scanning direction. A second synchronous scan of the reticle and substrate then results in a pattern exposed on the substrate that is congruent with the reticle pattern. Subsequent stepping and scanning operations can be used to copy an arbitrarily large pattern on a reticle to a similarly sized substrate using a xe2x88x921X relay having a smaller field size than the reticle pattern.